Treatment of petroleum products



Dec. 19, 1961 1. FERRARA ETAL TREATMENT OF' PETROLEUM PRODUCTS Filed Dec. 28, 1960 wmp-13mg United States Patent O M 3,013,965 TREATMENT F PETROLEUM PRDUCTS .lohn Ferrara and John E. Ryder, Chicago, Ill., assignors to Nalco Chemical Company, Chicago, Ill., incorporation of Delaware Filed Dec. ZS, 196i), Ser. No. 76,753 15 Claims. (Cl. 208-288) The present invention relates to the refining of petroleum, and more particularly to the chemical refining of petroleum including both crude petroleum and fractions produced from crude petroleum. Y

lIn the distillation of petroleum fractions from crude oils, many contaminants such as sulfur, nitrogen, phenolic and tnitrogenous bodies, acids, and complex organic molecules are carried overhead. These contaminants often give the various stocks undesirable physical and chemical characteristics. These undesirable characteristics include had odor, sourness to the conventional doctor test, poor color stability in storage', and formation of gumrny precipitates in storage. The presence of contaminants of the above type in gasoline fractions, for example, frequently reduces the clear octane value of the product as well as the lead susceptibility of the gasoline. The effects produced by harmful contaminants have recently become even more important due to the trend in the automotive industry toward higher engine horsepower and compression ratios. lt has also been found that modern methods of processing crude oil at high temperature und pressure conditions intensifies the undesirable effects caused by the impurities. y A number of processes are currently employed in an effort to improve the characteristics of gasoline, kerosene, and other petroleum fractions. Upgrading processes used by refiners today include caustic washing, acid treating, sweetening (conversion of mercaptan to disulfide) by numerous methods and hydroesulfurization. With the exception of caustic washing and acid treating, most available processes require considerable capital investment before the reiiner can go on stream. ln addition, the danger of caustic carryoverl is always present in caustic washing, and copper carryover is a threat ,in copper sweetening. Limited availability of excess hydrogen can be a problem in the use of the hydrodesulfurization process. rne acid treating process requires special considerations for waste disposal.

One of the criteria used in judging the quality of kerosene, gasoline, No. 1 fuel oil, and No. 2 fuel oil is the mercaptan content of the fraction as determined by the so-called doctor test. A doctor sweet` gasoline contains less than (l.0003-0.0006% by weight of mercaptan sulfur. lt is important to lower the mercaptain content of a petroleum fraction as low as possible not only from the standpoint of odor but because mercaptans have an adverse effect on octane number and lead susceptibility. Gasolines, kerosenes, etc., that are doctor sweet command a premium price in the industry.

It has -been found that the treatment of fractions with dilute or concentrated caustic solutions does not provide a doctor sweet product where the mercaptan content of the crude oil is appreciable. In other Words, it is impossible to produce a doctor sweet petroleum fraction consistently by presently known caustic treatment methods. It is particularly difficult to remove alkyl mercaptans from gasoline and other fractions by the use of caustic solutions.

tOne of the principal objects of the present invention, therefore, is to provide a method Which consistently will produce doctor sweet petroleum fractions.

Another object of the invention is to provide a method which will upgrade and stabilize the color of petroleum 3,013,965 Patented Dec. 19, 196,1

ICC

icl fractions and which will prevent the formation of insoluble matter on storage.

Another object is to provide a method which will improve the odor of petroleum fractions. n

Still another object of the invention is to provide a method of treatin-g gasoline, kerosenes, No. 2 fuel oils, etc., which can be carried out efficiently land economically.

Other objects will become apparent to those skilled in the art from the following detailed description of the invention.

In general, the invention comprises the discovery that unexpected improvements can be made in known refining methods by combining'the steps of (l) treating crude petroleum oil or a petroleum oil fraction with particular unsaturated polycarboxylic acid esters, and (2) thereafter contacting the oil with a particular alkaline material.

it has been found that the treatment of petroleum oil by the process described herein removes objectionable odors, renders the oil stable to a typical stability test (which comprises subjecting a sample of the oil in an open container to a temperature of 212 F, for 24 hours), and that the product consistently is doctor sweet. Moreover, the oil is stable and does not lose its color or form precipitates in storage.

The mechanism of the reactions which occur in the subject process is not fully understood, but it is believed that an addition reaction takes place between the unsaturated polycarboxylic acid ester and the inercaptans and other sulfur corn-pounds in the oil as well as with certain alcohols and nitrogen compounds which also may be present. Itis believed that the alkaline material serves as a catalyst for the addition reaction and causes the removal of phenolic bodies and other impurities from the oil. ln the treatment, some of the products of the 'addition reaction seem to remain in the oil, but without any apparent deleterious effect, while others are separated from the oil as sodium salts or soaps.` It should be understood, how-y ever, that this invention is not dependent upon any speciic reaction mechanism or theory.

The unsaturated polycarboxylic acid esters used as reagents in our process include esters of maleic acid, itaconic acid, fumarie acid, citraconic acid', mesaconic acid, and aconitic acid. Inasmuch as the acid component of the ester is believed to be primarily responsible for removing Vand converting the mercaptans, a'wide variety of alcohols can be used in preparing the materials. Aliphatic alcohols which can be esten'ed with the above acids can contain from 1 to about 12 carbon atoms. Alcohols having a chain length of 18 or more carbon atoms could also be used in preparing the esters. Such compounds are generally `more expensive `than the shorter chain materials, however, and would not provide any additional advantages. Specific alcohols include methyl alcohol, ethyl alcohol,.propyl alcohol, allyl alcohol, butyl alcohol, arnyl alcohol, hexyl alcohol, octyl alcohol, nonyl alcohol, decyl alcohol, and dodecyl alcohol. Aromatic alcohols such as benzyl alcohol and cyclic alcohols such as cyclohexyl alcohol can also be used in preparing the subject compounds. Specific esters that are more suitable for use in the process include dimethyl maleate, diethyl maleate, dipropyl maleate, diallyl maleate, dibutyl maleate, diamyl rnaleate, dioctyl maleate, didodecyl marleate, dimethyl itaconate, diethyl y Citraconie acid ester Aconitic acid ester Y where R, R1, and R2 are selected from the group consisting of an alkyl radical of from 1 to about 18 carbon atoms, a cycloalkyl radical, an aryl radical, and a substituted aryl radical.

In accordance with a preferred embodiment of this invention, the first treatment stage comprises thoroughly admixing with the oil a quantity of the above unsaturated ester and thereafter, Without intermediate settling or other processing, vigorously admixing with the oil containing the ester a quantity of concentrated aqueous alkali metal hydroxide solution.

The alkaline material may consist of a solution containing as little as about 3% alkali metal hydroxide. Preferably, however, the alkaline solution will contain from about 25% to about 50% NaOH or KOH. Stronger solutions of caustic alkali may be used but these tend to produce mechanical and handling diiculties particularly where low temperatures are encountered. In general, solutions containing at least 25% NaOH or KOH and preferably at least 35% NaOH or KOH are required for economical results. More dilute solutions require the use of much larger amounts of the unsaturated ester compounds if the process is to be successful. Although sodium hydroxide and potassium hydroxide are our preferred alkaline materials, barium hydroxide, calcium hydroxide, ammonium hydroxide, and other highly alkaline salts could serve as suitable substitutes. Additionally, it is possible to use solid alkaline materials in our process such as NaOH and KOH.

Where the oil to be treated is unusually sour, it is helpful to thoroughly admix a solution of sodium or potassium hydroxide with the oil before the unsaturated acid ester is introduced into the system. It has been shown that prewashing the oil with alkaline materials reduces the amount of soap formed in the process and also lowers the ester concentration which is required in the process. The concentration of the alkaline prewash solution also can vary from about 3% to about 50%.

Thedrawing constitutes a typical flow sheet illustrative of the ilow of oil and the reactants through the system in accordance with the method of this invention. The oil to be treated is fed through line 1 into mixer 2 wherein the oil is thoroughly admixed with a quantity of aqueous sodium or potassium hydroxide solution (a solution concentration of about is preferred) delivered to mixer 2 through line 3 from a suitable storage vessel 4. It should be realized, of course, that the pretreatment of the oil with the caustic solution can be eliminated if desired. Mixer 2 may be of any suitable form which is capable of thoroughly mixing the oil and alkaline solution. After leaving mixer 2, the mixture is passed through line 5 to a settling tank 6 wherein the oil is separated from the caustic 7. The treated oil, indicated at 8, collects on top of the caustic layer and above layer 9 which then contains certain impurities such as phenols, soaps, etc. The alkaline reagent is withdrawn from the bottom of vessel 6 through line 10 and is recirculated to mixer 2, make up sodium or posassium hydroxide solution being added from tank 4 as required. When the alkaline reagent is spent, it is withdrawn either continuously or intermittently from the recirculating alkali through line 11 for purification and reuse. The treated oil is withdrawn from the top of vessel 6 through line 12. impurities from layer 9 are withdrawn through line 13 and sent to a suitable place of disposition.

In the second and essential stage of the treatment, the oil is fed through line 12 to mixer 14 wherein the oil is thoroughly admixed with a small quantity of the unsaturated polycarboxylic acid ester. The ester is delivered to mixer 14 through line 15 from a suitable storage vessel 16. After a thorough mixing of the ester and oil is effected, the mixture is passed through line 17 to a third mixer 18 wherein the oil containing the ester is thoroughly agitated with a quantity of alkaline solution drawn through line 19 from storage vessel 20. Mixer 18 is of conventional form adapted to assure a thorough mixing of the oil and the second alkaline solution. The oil is then passed through line 21 to a settling vessel 22 wherein settling and stratification occur. The alkaline reagent indicated at 23 settles to the bottom; the soap products of the reaction form a layer indicated at 24, at the interface between the oil and alkaline reagent; and the treated oil indicated at 25 collects above the other layers. Due to the use of the caustic prewash, the amount of soap formed in the subsequent steps of the process is kept to a minimum. The soap reaction products which are considered as the impurities are withdrawn through line 26 and sent to a suitable place of disposition. The alkaline reagent is withdrawn from the bottom of vessel 22 through line 27 and recirculated to mixer 18, make up sodium hydroxide solution being added from tank 20 as required. A portion of the spent alkali may be withdrawn continuously or intermittently from the recirculating alkali through line 28 for purification and reuse. The treated oil is withdrawn from the top of vessel 22 through line 29 and sent to storage or to other processing units as may be desired.

The entire procedure is a liquid phase treating process which can be conducted at atmospheric temperatures and pressures, although where light gasoline distillates are treated the operation may be carried out in a closed system under sufficient pressure to prevent evaporation and loss of light fractions. The unsaturated polycarboxylic acid ester is added to the oil in proportion varying generally with the character and source of the oil to be treated.

In general, only a very small amount of the ester compounds is needed in the process. In terms of parts per million (ppm.) about 50 to 1,000 p.p.m. of the ester compounds will suflice in most cases. Straight run gas oil or lighter distillates from relatively sweet crudes require the minimum quantities. Where the fraction is from sour crudes or from catalytic cracking operations, particularly those relatively high in sulfur compounds, phenolic and nitrogenous bodies, and organic acids, however, as much as 10,000 ppm. may be required in certain instances. Correspondingly, where very dilute solutions of sodium hydroxide, for example, are used as catalysts in the process as much as 100,000 p.p.rn. of the ester may then be needed. Our broad range of ester concentration, therefore, is from to about 100,000 p.p.m. while our preferred range is from about 50 to 1,000 ppm. where the second alkali h-ydroxide solution contains at least about 25% alkali hydroxide. As was indicated above, the amount of ester required in the method is considerably reduced where the oil is prewashed with a caustic solution.

The second addition of the alkaline solution to the oil is made immediately following the addition of the ester to the petroleum. The time interval between the addition to the oil of the ester and the alkaline solution is variable, it being only important that the ester be thoroughly mixed with the oil before the alkaline solution is added thereto. While the alkaline material ordinarily will be added immediately after the completion of the mixing of the ester and the oil, the treatment may be successfully effected even though the alkali metal hydroxide or other alkaline material is added hours or days after the addition of the ester yto the oil.

It appears that whatever may be the reactions which occur between the ester and the constituents of the oil, these reactions occur substantially instantaneously so that it is only necessary to employ suiiicicnt mixing to assure that the ester has been thoroughly distributed throughout the oil before the alkali solution is applied. It is important to note, therefore, that the reagents should be added separately and successively, the second treatment with the alkali solution following the ester addition, but that the time interval between the additions of the reagents is not particularly important.

- The alkaline solution used in theinitial step is preferably one which contains about 5% alkali metal hydroxide. It is'possible, however, to luse solutions containing from as little as 3% alkali up to as much as 50% alkali. The lower concentrations are preferred for removing acidic materials while the more concentrated solutions have a greater capacity for RSI-I (mercaptan) removal. As was pointed out above, the second alkaline treatment solution preferably contains at least 25% and more preferably 40% to 50% alkali.

The treated oil which is drawn off from the upper portion of settler 22 is found to be free of undesirable odors, is completely stable to the standard stabilit-y test described above, and is consistently sweet to the doctor test regardless of the nature of the crude oil.

kThe amount of alkaline reagent addedv to the mixture of oil and anhydride should be sulcient to insure intimate Contact between the reagents. The volume of the alkaline solution used in both the pretreatment and the nal treatment can be varied over a wide range. Usually, this range would be between about 0.5% and about 100% basedvon the volume of the oil. Much larger amounts, however, could be used without diiculty. In practice, the use of 5% by volume of the alkaline solution based on the volume of the oil has been found to be satisfactory. Ifa longer time of treatment is used, a lower vvolume percentage of the alkaline reagent can be employed. Correspondingly, if a highly eicient agitating means is employed, the volume of the alkaline solution needed to produce satisfactory results is significantly lowered. In fact, as little as 0.001% of caustic added to the mixture of oil and ester has provided morethan adequate contact between the reagents. The use vof less alkali also is advantageousin that a smaller amount of precipitated salts are thereby producedr during the contact period.

'Ihe time of treatment of the oil with the ester should be suicient to insure adequate mixing and will vary somewhat depending on vthe volume of oil treated.V

'to be catalyzed by the presence of the alkaline solution and take place quite rapidly.

In the second treatment of the alkaline reagent, the

time of contact should be sufficient to neutralize the acids in the oil. As a practical matter, the time of treatment can be determined by withdrawing samples of the reaction mixture and testing them to ascertain whether they break properly and whether the oil phase is substantially free from the alkaline reagent. When the alkaline reagent consists of a solution of alkali metal hydroxide and water, a sample drawn in a four ounce bottle to which a few drops of an indicator, such as phenoethalein is added, will show tiny red specks if dispersed caustic is present in the oil. If more than a few such specks are present, it is an indication that too much caustic has been added or that the time of contact was -too great. In general, the time of contact with the alkaline reagent is quite short, eg., one to two seconds to five minutes in the mixing step. In the pretreatment of the oil with the alkaline solution, the time of contact can range from about one to two seconds to 30 minutes or more. It has been found that a contact time of about 15 seconds is satisfactory for most purposes.

The temperature Vat which the oil is held during the process is subject to variation but good results have been obtained by operating at ordinary temperatures and pressures. Temperatures of F. to 110 F., preferably F. to 105 F., have proven to be very satisfactory but higher temperatures, say F. to 200 F., can be used. The alkali-oil contact temperatures are in the same range as those given for the ester.

The process'above described may be applied directly to crude petroleum before it is charged to the crude stills, in which instance the oil leaving the settler 22 when subjected to the usual distillation process, will produce distillate fractions, namely, gasoline, kerosene, and light gas oil, which will be found to be improved in several respects. vThe gasoline fractions will usually be found to have maximum clear octane values and maximum lead susceptibility as compared with the stocks from the same crude subjected to the same type of distillations, but without previous treatment of the kind described above. Moreover, the kerosene and light `gas oil fractions which ordinarily go into the burning oils will have good burning qualities, will be free of undesirable odors, and will be completely stable in storage. In many cases the treated crude itself will be reduced in odor, be more stable and when used as a fuel will have improved burning characteristics.

The same character of improvement will be noted when treating straight run, thermally cracked, or catalytically cracked gas oils which are to be used for burning oils.

The following examples illustrate the practice of the invention.

Example I As was lpointed out above, the presence of sulfur compounds, and especially mercaptans, in gasoliners 'and other petroleum fractions is undesirable `because of their odor, because they contribute to noxious engine exhaust and engine corrosion, and because ofthe adverse effect that they have on octane numbers and lead susceptibility. In this illustrative example, several petroleum fractions were subjected nto the doctor testafter being treated by the subject process. In each instancethe frac tion had a noxious odor and was sour to the doctor test prior to the treatment. The method consisted of adding a given quantity of an unsaturated polycarboxylic acid ester (in these tests the ester was diethyl maleate) to the hydrocarbon with suflicient agitation to insure that the chemical ywent into solution. The hydrocarbon was then agitated with a 50% alkali (NaOH) solution and allowed to settle. Within seconds after the completion of the agitation, samples of the various fractions were subjected to the doctor test.

Example I1 In these tests, a No. l fuel oil was treated with 500 ppm. of diethyl maleate and then passed through a column of either solid NaOH pellets or solid KOH pellets. ln each instance, the resultant product was doctor sweet.

Example III This example illustrates the effectiveness of various esters and of caustic solutions of varying concentrations in the subject process. In each test, either a No. 1 fuel oil that had a noxious odor and was sour, or a kerosene that was sour, was treated with the ester with sufficient agitation to place the chemical in solution and was then contacted with the caustic solution. The samples were tested within seconds after the caustic was added.

Petroleum Esters Quantity, Percent Results Fraction ppm. NaOH No. 1 fuel oil Dibutyl malcate 300 50 Diallyl maleate. 500 45 Dimethyl itaconate 1,000 35 500 40 300 60 150 50 Do. Didodecyl fumarate. 500 40 Do. Diethyl maleate.. 700 50 Do. .do 800 45 Do ,do.- 1,600 40 Dn ..,do 22,000 30 Do d 50,000 20 Do do 113,000 10 Do The above tests that were run at a low caustic concentration indicate that while the process will work at these concentrations, more concentrated solutions greatly increase the eiliciency of the process.

Example IV sweet product as is shown by the following table:

Caustic Brew-ash Ester Con- Results centration None 900 Sour. Nona... 1,000 Doctor sweet. 5% NaOH- 800 Do. 45% NaOH 500 Do.

The above results also show that as the caustic concentration in the pretreatment step increases, the quantity 8 of ester needed to produce a doctor sweet stock decreases.

Example V This example illustrates the effectiveness of the subject method in improving the stability and odor of fuel oils. In these tests, diethyl maleate was used as the ester and the process was carried on as described in Example I.

After Accelerated Storage Test (24 hours at 212 F.) Concentration, Diethyl Odor Maleate Color 1 Sludge (a) untreated Poor..- Yes. (b) 200 p.p.m. DEM Excelle No.

(a) untreated Poor 8 Yes. (b) 500 p.p.m. DEM Excelient Lighter than 2.- No.

1 Diethyi maleate.

2 Color union colorimetei` scalo. A color of 2% after accelerated storage test is maximum acceptable to meet commercial specifications. The color 8 is the maximum obtainable on the union scale and corresponds to a cherry red. The color before accelerated storage in each case was lighter than 2.

1 Formation of insoluble materials formed from oil.

Example VI In these tests, No. 1 fuel oils were treated with various amounts of diethyl maleate and with a 40% concentration of sodium hydroxide n order to determine the elect of the present invention on the color of petroleum oil fractions.

Color after heating Color at 212F. for 24 hours Treatment Original Aitor Color 1 Treating Un- Treated treated 1 Saybolt color scale.

As is apparent from the above table, the use of the ester and caustic treatment both upgraded and stabilized the color of the fuel oil.

The present invention provides an effective, low cost process for the treatment of hydrocarbon fractions which consistently renders the products doctor sweet. The use of a caustic prewash is helpful in treating unusually sour crudes in that it reduces the quantity of soaps produced and the amount of ester needed in the process.

As was pointed out above, the ester is formed from unsaturated polycarboxylic acids such as maleic acid, itaconic acid, fumarie acid, citraconic acid, mesaconic acid, or aconitic acid. Because the acid component'of the ester is primarily responsible for removing and converting mercaptans, a wide variety of alcohols can be used in preparing the treating agents. Aliphatic alcohols containing from 1 to 18 carbon atoms can be esterified with the above acids 'to prepare our products. Aromatic alcohols such as benzyl alcohol and cyclic alcohols such as cyclohexyl alcohol can be used in place of the aliphatic alcohols. Due to its availability and low cost, dibutyl maleate is our preferred reactant. For the same reasons, esters of aliphatic alcohols containing from l to 5 carbon atoms are preferred over other esters.

The doctor sweet test referred to herein is a standard test method described in the publication, UOP Laboratory Test Methods for Petroleum and Its Products, 3rd edition, Universal Oil Products Company, 1948, pages H21-22.

Obviously many modications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

The present application is a continuation-in-part of our copending application Serial No. 5,588, filed February 1, 1960, now abandoned.

The invention is hereby claimed as follows:

l. A method of refining petroleum oil which comprises: admixing with a petroleum oil stock in the liquid phase an ester of an acid selected from the group consisting of rnaleic acid, itaconic acid, fumarie acid, citraconic acid, mesaconic acid, and aconitic acid in a minimum amount of at least p.p.m. by weight of the oil; agitating the admixture with an alkaline material; and thereafter separating the treated oil from the resultant mixture.

2. A method of refining petroleum oil which comprises: admixing with a petroleum oil stock in the liquid phase an ester of an acid selected from the group consisting of maleic acid, itaconic acid, fumarie acid, citraconic acid, mesaconic acid, and aconitic acid in a minimum amount of at least 10 to about 100,000 ppm. by weight of the oil; agitating the admixture with an alkaline material; and thereafter separating the treated oil from the resultant mixture.

3. A method of refining petroleum oil which comprises: admixing with a petroleum oil stock in the liquid phase an ester of an acid selected from the group consisting of maleic acid, itaconic acid, fumarie acid, citraconic acid, mesaconic acid, and aconitic acid in a minimum amount of at least 50 to about 1,000 ppm. by weight of the oil; agitating the admixture with an alkaline material; and thereafter separating the treated oil from the resultant mixture.

4. A method of refining petroleum oil which comprises: admixing with a petroleum oil stock in the liquid phase an ester of an acid selected fromthe group consisting of maleic acid, itaconic acid, fumaric acid, citraconic acid, mesaconic acid, and aconitic acid in a minimum amount of at least 50 to about 1,000 ppm. by weight of the oil; agitating the admixture with a concentrated alkali hydroxide solution containing at least 25% by weight of alkali hydroxide; and thereafter separating the treated oil from the resultant mixture.

5. A method of refining petroleum oil which comprises: admixing 'with a petroleum oil stock in the yliquid phase an ester of an acid selected from the group consisting of maleic acid, itaconic acid, fumarie acid, citweight of the oil; agitating the admixture with a concentrated alkali hydroxide solution containing from about 40% to about 50% by weight of alkali hydroxide; and thereafter separating the treated oil from the resultant mixture.

6. A method ot' refining petroleum oil which comprises: admixing with a petroleum oil stock in the liquid phase from about 10 to 10,000 ppm. of an ester prepared by reacting an acid selected from the group consisting of maleic acid, itaconic acid, fumarie acid, citraconic acid, mesaconic acid, and aconitic acid with an alcohol selected from the group consisting of aliphatic alcohols of from. 1 to about 18 carbon atoms, cycloalkyl alcohols, aryl alcohols, and substituted aryl alcohols; agitating the admixture with an alkali hydroxide solution; and thereafter separating the treated oil from the resultant mixture.

7. A method of refining petroleum oil as in claim` 3 wherein the petroleum oil stock is gasoline.

8. A method of refining petroleum oil as in claim 3 wherein the petroleum oil stock is kerosene.

9. A method as in claim 3 wherein the ester is dimethyl maleate. Y

10. A method as in claim 3 wherein the ester is diet'hyl maleate.

11. A method as in claim 3 wherein the ester is dipropyl maleate.

12. A method as in claim 3 wherein the ester is diisopropyl maleate.

13. A method as in claim 3 wherein the ester is dialiyl maleate. v

l4. A method as in claim 3 wherein the ester is dibutyl maleate.

l5. A method of refining petroleum oil which comprises: admixing with a petroleum oil stock in the liquid phase an aqueous alkali hydroxide solution containing from about 3.0% to about 50% by weight of alkali hydroxide; separating the treated oil from the caustic; admixing said petroleum oil stock with from about 50 to about 1,000 ppm. yof an ester of an acid selected from the group consisting of maleic acid, itaconic acid, fumarie acid, citraconic acid, mesaconic acid, and aconitic acid; agitating the admixture with a concentrated aqueous alkali hydroxide solution containing at least about 25% by weight of alkali hydroxide, the Volume of said alkali hydroxide being sufficient to obtain intimate mixing; and thereafter separating the treated oil from the resultant mixture.

No references cited. 

2. A METHOD OF REFINING PETROLEUM OIL WHICH COMPRISES: ADMIXING WITH A PETROLEUM OIL STOCK IN THE LIQUID PHASE AN ESTER OF AN ACID SELECTED FROM THE GROUP CONSISTING OF MALEIC ACID, ITACONIC ACID, FUMARIC ACID, CITRACONIC ACID, MESACONIC ACID, AND ACONITIC ACID IN A MINIMUM AMOUNT OF AT LEAST 10 TO ABOUT 100,000 P.P.M. BY WEIGHT OF THE OIL, AGITATING THE ADMIXTURE WITH AN ALKALINE MATERIAL, AND THEREAFTER SEPARATING THE TREATED OIL FROM THE RESULTANT MIXTURE. 